nanomath/src/number/arithmetic.js

import {plain} from './helpers.js'
import {NumberT} from './NumberT.js'
import {OneOf, Returns, ReturnTyping, Undefined} from '#core/Type.js'
import {match} from '#core/TypePatterns.js'
import {Complex} from '#complex/Complex.js'
import {ReturnsAs} from '#generic/helpers.js'

const {conservative, full} = ReturnTyping

export const abs = plain(Math.abs)
export const norm = abs
export const normsq = plain(a => a*a)
export const add = [
   plain((a, b) => a + b),
   match([Undefined, NumberT], Returns(NumberT, () => NaN)),
   match([NumberT, Undefined], Returns(NumberT, () => NaN))
]
export const divide = plain((a, b) => a / b)
const numberCbrt = a => {
   if (a === 0) return a
   const negate = a < 0 
   if (negate) a = -a
   let result = a
   if (isFinite(a)) {
      result = Math.exp(Math.log(result) / 3)
      result = (a / (result * result) + (2 * result)) / 3
   }
   return negate ? -result : result
}
const cbrtIm = Math.sqrt(3) / 2
export const cbrt = match(NumberT, (math, _N, strategy) => {
   if (strategy === full && math.types.Complex && math.types.Vector) {
      // return vector of all three complex roots, real one first
      const C = Complex(NumberT)
      const vec = math.vector.resolve([C, C, C])
      const promote = math.complex.resolve([NumberT])
      const cplx = math.complex.resolve([NumberT, NumberT])
      return ReturnsAs(vec, x => {
         const realroot = numberCbrt(x)
         if (!isFinite(realroot)) {
            const full = cplx(realroot, realroot)
            return(promote(realroot), full, full)
         }
         return vec(promote(realroot),
            cplx(-realroot / 2, realroot * cbrtIm),
            cplx(-realroot / 2, -realroot * cbrtIm))
      })
   }
   return Returns(NumberT, numberCbrt)
})

export const invert = plain(a => 1/a)
export const multiply = [
   plain((a, b) => a * b),
   match([Undefined, NumberT], Returns(NumberT, () => NaN)),
   match([NumberT, Undefined], Returns(NumberT, () => NaN))
]
export const negate = plain(a => -a)

export const sqrt = match(NumberT, (math, _N, strategy) => {
   if (!math.types.Complex || strategy === conservative) {
      return Returns(NumberT, Math.sqrt)
   }
   const cplx = math.complex.resolve([NumberT, NumberT], full)
   if (strategy === full) {
      const cnan = math.nan(Complex(NumberT))
      return Returns(Complex(NumberT), a => {
         if (isNaN(a)) return cnan
         return a >= 0 ? cplx(Math.sqrt(a), 0) : cplx(0, Math.sqrt(-a))
      })
   }
   // strategy === free, return "best" type
   return Returns(OneOf(NumberT, Complex(NumberT)), a => {
      if (isNaN(a)) return NaN
      return a >= 0 ? Math.sqrt(a) : cplx(0, Math.sqrt(-a))
   })
})

export const subtract = [
   plain((a, b) => a - b),
   match([Undefined, NumberT], Returns(NumberT, () => NaN)),
   match([NumberT, Undefined], Returns(NumberT, () => NaN))
]

export const quotient = plain((a,b) => Math.floor(a/b))